and applying the stationary phase formula ([1]}), we obtain
\(1 \cong -k \sqrt{\frac{\pi m^3}{kN \dot{m}}} \frac{2 m f}{k N} \Big [\frac{1}{2 \pi } \frac{\Vert  \Upsilon _z(M_r) \Vert  }{\sqrt{M_r}}\Big ] \cos (\pm \frac{\pi }{4} + \vartheta (t_0)) \; ,\) 
